# CoreXY Carriage moves on the Y when moving the X

I have a custom designed and built CoreXY printer. I have noticed that when I order the X to move from one side to the other (right to left) that the Y axis moves back about 0.6 mm as well. When I move the X back (from left to right) the Y also moves forward approximately the same amount.

What property of the CoreXY system could be causing this? Note, I am using 608 bearings instead of toothed idler pulleys; which I hope to rectify soon.

Steps per mm from the Marlin configuration.h:

DEFAULT_AXIS_STEPS_PER_UNIT   { 475.79, 482.87, 468.66, 188.1 }


Note, they are not the same for X and Y. This is because I am trying to run a calibration cube test on the machine.

• that sounds like either a firmware or a hardware problem... – Trish Oct 25 '19 at 21:26
• Is the motor turning causing the movement? Or is this a measurement you've taken for the y-axis travel? – Pᴀᴜʟsᴛᴇʀ2 Oct 25 '19 at 22:50
• @Paulster2, This is a measurement I've taken for the y-xis travel; – user77232 Oct 26 '19 at 12:03
• Are the steps per mm for X and Y set to the same value? – Tom van der Zanden Oct 26 '19 at 12:12
• @user77232 it could be a pinning error (as in the firmware pins are messed up) or steps/mm (which is in the firmware). try to check hardware first. – Trish Oct 26 '19 at 12:24

It is therefore highly illogical that you need to use different values for your steps per mm (X = 475.79 steps/mm, Y = 482.87 steps/mm). If you need to use such values, this implies that your mechanical layout/mechanics is/are incorrect (skew frame, different pulley diameters, slip on pulley, incorrect tension of belts, etc.). It is advised to make them equal and check the mechanical layout and inspect all parts (pulley diameters) and make the tension equal (e.g. using a Belt Tension Gauge). If the head still moves in the perpendicular direction as commanded, you could try to calibrate from there.